Exactly, it's one of the things we do most correctly. It's inefficient and it works worse under ideal conditions. But a government shouldn't be a finely tuned machine that only works when everything is going right. It's a lumbering mess that's going to be sabotaged, poorly stewarded, and have maintenance deferred. It's your daily driver car and you probably ain't both rich (and sure you'll stay that way) and the sort excited to spend all your time working on it. A Porsche will just give you problems when you defer maintenance, what you want is the Honda or Toyota best fit to your needs with the bells and whistles you really need. Jury trial is the justice system for that.

It forces the government to get the consent of the governed before it sentences anyone to anything. If the grand jury says "these charges are vindictive bullshit" they can stop a trial from even happening. If they let it through then another set of 12 citizens have to be convinced (beyond a reasonable doubt if it's criminal, which would be prosecuted by the government, or a preponderance of the evidence if it's a civil trial, which is prosecuted by the victim). And that's why Trump keeps pushing to reduce jury trials.